An experiment in privacy–and the discussion that ensued–offer unexpected lessons in who gets watched, and how.

This story is part of The Privacy Divide, a series that explores the fault lines and disparities–economic, cultural, philosophical–that have developed around data privacy and its impacts on society.

“And so STRESS [Stop the Robberies, Enjoy Safe Streets] was born. With the help of computer data, [Detroit police commissioner John] Nichols planned to flood the streets with undercover cops disguisedas drunks and priests, hippies and elderly women. When robbers tried to hold up these “decoys,” backup officers would swoop in and make an arrest. As Nichols explained to the congressional committee, his department hoped to “perfectly blend men into the environment” on a scale never before attempted. “With STRESS,” he testified, “the criminal must fear the potential victim.”

Being surveilled has been, and continues to be, the de-facto state of existence for marginalized populations in America, and not coincidentally, in private is often where movements within those communities start and where they gain momentum and power. This was made clear to me by my parents, early on in my life. Growing up in Detroit, under the specter of STRESS, there was the sense that my neighborhood, my community, was always under a watchful eye whose purpose was not to protect me but to protect others from me and people who looked like me.

Privacy for marginalized populations has never been, and will never be an abstract. Being surveilled, whether by private actors, or the state, is often the gateway to very tangible harms–violence in the form of police brutality, incarceration, or deportation. And there can be more subliminal, insidious impacts, too.

“The fear and uncertainty generated by surveillance inhibit activity more than any action by the police,” Joshua Franco, a senior research adviser and the deputy director of Amnesty Tech at Amnesty International, told Motherboard last year. “People don’t need to act, arrest you, lock you up and put you in jail. If that threat is there, if you feel you’re being watched, you self-police, and this pushes people out of the public space. It is so hard to operate under those types of conditions.”

Which brings me to a recent op-ed in the New York Times about a thought-provoking lesson in privacy. Kate Klonick, an assistant professor at St. John’s University Law School, described an optional and ungraded assignment in which she asked her students to eavesdrop on and surveil unsuspecting folks in public to see what information they could gather about them, using only Google search on their phones.

The point, Klonick wrote, was “to demonstrate to my students how the most common of technologies can be used to shatter the perceived protections of obscurity and, in turn, reveal the admittedly thin mechanisms by which privacy is actually protected.”

Some students told her the idea was “creepy.” “I assured them that the goal was not to eavesdrop on a purposefully private conversation,” she wrote, “or to do any ‘digging’ on the person, or to share or do anything with the information they found out. This was to be purely an exercise in whether people can actually be private in public places and whether they expect to be.”

The assignment was widely discussed, and Klonick appeared on NPR and CNN to describe the impact of the experiment on her students. “Most significantly,” she wrote in a Twitter thread that went viral, “a number who had clung to the idea of ‘I don’t care if anyone’s watching, I have nothing to hide’ were shocked into seeing the privacy issues. Including a future district attorney.”

Others, however, were shocked in different ways. “Folks, this is wrong,” Les Hutchinson, a PhD candidate who studies surveillance impacts on Chicana and Indigenous women, wrote on Twitter. “Do not make your students reproduce the conditions of privacy violations to teach them about privacy violations without the consent of those being violated.”